1. Field of the Invention
The present invention relates to a method of driving an AC plasma display panel (hereinafter also referred to as “AC-PDP”), an AC-PDP and a plasma display device, and more particularly, it relates to a technique for reducing the cost for a plasma display device.
2. Description of the Background Art
Various researches are made on plasma display panels (PDP) as thin-type television or display monitors. AC-PDPs having memory functions include a surface discharge AC-PDP. The structure of this AC-PDP is now described with reference to FIG. 10.
FIG. 10 is a perspective view extracting and showing part of the structure of an AC-PDP 101 according to first background art. For example, Japanese Patent Application Laid-Open No. 7-140922 (1995) or Japanese Patent Application Laid-Open No. 7-287548 (1995) discloses an AC-PDP having such a structure. As shown in FIG. 10, the AC-PDP 101 comprises a front glass substrate 102 serving as a display surface and a rear glass substrate 103 opposed to the front glass substrate 102 through discharge spaces 111. While the glass substrates 102 and 103 are so arranged that the top portions of barrier ribs 110 are in contact with a dielectric layer 106A described later, FIG. 10 illustrates the glass substrates 102 and 103 in a separated state for convenience of illustration.
On a surface of the front glass substrate 102 closer to the discharge spaces 111, n row electrodes 104 and n row electrodes 105 (both are transparent electrodes) paired with each other are extended/formed. When metal auxiliary electrodes (also referred to as “bus electrodes”) 104a and 105a having low impedance for supplying a current from a circuit part are provided on partial surfaces of the row electrodes 104 and 105 respectively as shown in FIG. 10, the respective ones are referred to as “row electrodes 104” and “row electrodes 105” inclusive of the metal auxiliary electrodes respectively. The dielectric layer 106 is formed to cover both row electrodes 104 and 105. A protective film 107 of a dielectric substance such as MgO (magnesium oxide) may be formed on the surface of the dielectric layer 106 by a method such as vapor deposition as shown in FIG. 10, and the dielectric layer 106 and the protective film 107 are also generically referred to as “dielectric layer 106A” in this case.
On the surface of the rear glass substrate 103 closer to the discharge spaces 111, on the other hand, m column electrodes 108 are extended/formed to (grade-separately) intersect with the row electrodes 104 and 105, and the barrier ribs 110 are extended/formed between the adjacent ones of the column electrodes 108 in parallel with the column electrodes 108. The barrier ribs 110 separate respective discharge cells from each other while supporting the AC-PDP 101 not to be crushed under the atmospheric pressure.
A phosphor layer 109R for emitting red (R) light, a phosphor layer 109G for emitting green (G) light and a phosphor layer 109B for emitting blue (B) light (these phosphor layers 109R, 109G and 109B are also referred to as “phosphor layers 109”) are arranged in U-shaped trenches defined by the aforementioned surface of the rear glass substrate 103 and opposite side wall surfaces of the adjacent barrier ribs 110 in prescribed order to cover the column electrodes 108 in the form of stripes. There is also an AC-PDP having such a structure that a dielectric layer is provided on the aforementioned surface of the rear glass substrate 103 to cover the column electrodes 108 so that the barrier ribs 110 and the phosphor layers 109 are arranged on this dielectric layer.
The front glass substrate 102 and the rear glass substrate 103 having the aforementioned structures are sealed to each other along peripheral edge portions (not shown in FIG. 10) so that spaces (the discharge spaces 111) between the glass substrates 102 and 103 are filled with discharge gas such as an Ne—Xe gas mixture or an He—Xe gas mixture under pressure below the atmospheric pressure. In the AC-PDP 101, the grade-separate intersection between each pair of row electrodes 104 and 105 and each column electrode 108 defines a discharge cell (also referred to as “luminous cell” or “display cell”). In a full color display PDP such as the AC-PDP 101, three discharge cells for emitting red light, green light and blue light form a single pixel. In this case, FIG. 10 shows the structure of the AC-PDP 101 for the single pixel.
In the following description, a transverse line of a luminous color obtained by lighting luminous cells of all luminous colors or arrangement of pixels necessary for displaying the transverse line is referred to as “display line”. The AC-PDP 101 can light or select (discharge cells belonging to) a single display line when applying a prescribed voltage to a pair of row electrodes 104 and 105. Such arrangement that three discharge cells forming a single pixel are transversely aligned with each other may also be referred to as “stripe arrangement”.
In the AC-PDP 101, the discharge spaces 111, divided by the barrier ribs 110, extending along the longitudinal direction of the column electrodes 108 can be separated into (i) “luminous area” or “display area” forming discharge cells to which the pairs of electrodes 104 and 105 belong and (ii) “non-luminous area” or “non-display area” between an adjacent pair of electrodes 104 and 105 (or each adjacent area of a plurality of discharge cells arranged along the aforementioned longitudinal direction) irrelevant to display luminescence of the PDP. In the following description, the structure forming the non-luminous area in the discharge spaces 111, i.e., the structure between discharge cells adjacent along the longitudinal direction of the column electrodes 108 is referred to as “non-discharge cell (or non-luminous cell or non-display cell)” with respect to the luminous area forming the discharge cell for convenience.
Among gaps between the adjacent row electrodes 104 and 105, (i) a gap between two row electrodes 104 and 105 forming discharge in the discharge cell in a paired manner is referred to as “discharge gap DG” while (ii) a gap between two opposite row electrodes 104 and 105 belonging to adjacent discharge cells respectively is referred to as “non-discharge gap NG”. While the non-discharge cell has the discharge space 111 (non-discharge area) defined by the intersection between two row electrodes 104 and 105 (belonging to adjacent discharge cells respectively) and the column electrode 108 similarly to the discharge cell, the distance between the non-discharge gaps NG is so widely set as not to cause discharge in the AC-PDP 101.
An AC-PDP 201 according to second background art is now described with reference to FIGS. 11 and 12. FIG. 11 is a plan view of the AC-PDP 201 according to the second background art, and FIG. 12 is a longitudinal sectional view taken along the line I—I in FIG. 11. For example, Japanese Patent Application Laid-Open No. 6-12026 (1994) discloses an AC-PDP having such a structure. As shown in FIGS. 11 and 12, the AC-PDP 201 comprises a front glass substrate 202 serving as a display surface and a rear glass substrate 203 opposed to the front glass substrate 202 through discharge spaces 211. Row electrodes 204 and 205 are alternately formed on the surface of the front glass substrate 202 closer to the discharge spaces 211 at regular intervals. The row electrodes 204 and 205 may be formed by combination of transparent electrodes and bus electrodes similarly to the aforementioned AC-PDP 101, and the electrodes consisting of transparent electrodes and bus electrodes are also referred to as “row electrodes 204 and 205” in this case. A dielectric layer 206 and a protective film 207 (also generically referred to as “dielectric layer 206A”) are successively formed on the row electrodes 204 and 205.
Column electrodes 208 are extended/formed on the rear glass substrate 203 to (grade-separately) intersect with the row electrodes 204 and 205, and a dielectric layer 212 is formed to cover the column electrodes 208. The glass substrates 202 and 203 are opposed to each other through barrier ribs 210. As shown in FIG. 11, the space between the glass substrates 202 and 203 is divided into a plurality of hexagonal discharge spaces 211 by the glass substrates 202 and 203 and the barrier ribs 210. The barrier ribs 210 are so arranged that the centers of the respective discharge spaces 211 substantially match with the intersections of the gaps between the adjacent row electrodes 204 and 205 and the column electrodes 208 in the plan view shown in FIG. 11. In the AC-PDP 201, the respective gaps between the adjacent row electrodes 204 and 205 define discharge gaps DG, with no presence of non-discharge gaps, i.e., non-discharge cells. Thus, each discharge cell defined by the intersection between each pair of row electrodes 204 and 205 and each column electrode 208 is enclosed with the barrier ribs 210 and separated from adjacent discharge cells in the AC-PDP 201. As shown in FIG. 11, each column electrode 208 consists of a part opposed to the discharge spaces 211 and a part opposed to the barrier ribs 210, and these parts are alternately repeated at a pitch half that of the discharge cells arranged along the longitudinal direction of the column electrodes 208.
Phosphor layers 209 of the same luminous color are applied onto the dielectric layer 212 and to (parts of) the side wall surfaces of the barrier ribs 210 in the plurality of discharge cells arranged along each column electrode 208. In other words, a plurality of discharge cells for a luminous color of red (R), green (G) or blue (B) are arranged along each column electrode 208. In other words, each column electrode 208 corresponds to a single luminous color (or display color). In the AC-PDP 210, therefore, three discharge cells (FIG. 11 shows exemplary arrangement by symbols R, G and B) for respective luminous colors arranged in the form of a delta form a pixel for white display, and such arrangement of the discharge cells may also be referred to as “delta arrangement”. The remaining structure such as discharge gas is similar to that of the first background art.
The display operation principle of the aforementioned AC-PDP 101 (or 201) is now described. First, a voltage pulse is applied across the pair of row electrodes 104 and 105 (or 204 and 205) for causing discharge. Ultraviolet rays resulting from this discharge excite the phosphor layers 109 (209) so that the discharge cells luminesce. Electrons and ions generated in the discharge spaces during this discharge move toward the row electrodes 104 and 105 (204 and 205) having opposite polarity thereto and are stored on the surface of the dielectric layer 106A (206A) located on the row electrodes 104 and 105 (204 and 205). Charges such as the electrons and ions thus stored on the surface of the dielectric layer 106A (206A) are referred to as “wall charges”.
An electric field formed by the wall charges acts to weaken an electric field formed by the voltage applied across the row electrodes 104 and 105 (204 and 205), and hence the discharge rapidly disappears following formation of the wall charges. When applying a voltage pulse reversed in polarity across the row electrodes 104 and 105 (204 and 205) after the discharge disappears, discharge can be caused again since an electric field formed by superposition of the applied electric field and an electric field formed by wall charges is substantially applied to the discharge spaces. Thus, once discharge is caused, discharge can be caused again by applying a lower applied voltage (hereinafter also referred to as “sustain voltage”) than the firing voltage, whereby discharge can be stationarily sustained by successively applying sustain voltages (hereinafter also referred to as “sustain pulses”) reversed in polarity across the row electrodes 104 and 105 (204 and 205). This discharge is hereinafter referred to as “sustain discharge”.
This sustain discharge is maintained so far as the sustain pulses are applied until the wall charges disappear. An operation of making the wall charges disappear is referred to as “erasing”, while an operation of forming wall charges on the dielectric layer 106A (206A) in the initial stage of discharge is referred to as “writing”. Therefore, characters, figures, images and the like can be displayed by first performing writing on arbitrary discharge cells on the screen of the AC-PDP and thereafter performing sustain discharge. Further, motion pictures can also be displayed by performing writing, sustain discharge and erasing at a high speed.
A more specific method of driving the conventional PDP is now described with reference to FIG. 13. For example, Japanese Patent Application Laid-Open No. 7-160218 (1995) (or Japanese Patent No. 2772753) discloses a method of driving the conventional AC-PDP 101 (see FIG. 10). FIG. 13 is a timing chart showing waveforms of driving voltages in a single subfield (SF) in the driving method. In the following description, each of n row electrodes 104 is referred to as “row electrode Xi” (i=1 to n) and each of n row electrodes 105 is referred to as “row electrode Yi” (i=1 to n), while n row electrodes Y1 to Yn are collectively referred to as “row electrodes Y” assuming that all row electrodes Y1 to Yn are driven with a single driving signal (voltage). Further, each of m column electrodes 108 is referred to as “column electrode Wj” (j=1 to m).
The subfield (SF) shown in FIG. 13 is one of a plurality of periods obtained by dividing a single frame (F) for image display. The subfield is further divided into three periods, i.e., “reset period”, “address period” and “sustain discharge period (also referred to as a sustain period or a display period)”.
In the “reset period”, a display history at an end point of a preceding subfield is erased while priming particles for improving discharge probability in the subsequent address period are supplied. More specifically, a full writing pulse Vp having a voltage value capable of causing self-erase discharge on the trailing edge thereof is applied across all row electrodes X1 to Xn and row electrodes Y thereby erasing the display history. At this time, a voltage pulse Vp1 is applied to the column electrode Wj.
In the “address period”, only discharge cells to be displayed are selectively discharged by selecting a matrix for forming “address discharge” on the discharge cells. More specifically, a scan pulse Vxg (voltage value Vxg (<0)) is successively applied to the row electrodes Xi and a voltage pulse VwD (voltage value VwD (>0)) based on image data is applied to the column electrode(s) Wj in the discharge cell(s) to be lighted, thereby causing “writing discharge” between the column electrode Wj and the row electrode Xi, as shown in FIG. 13. During the address period, a subscan pulse Vysc (voltage value Vysc (>0)) is applied to the row electrodes Y. At this time, a potential difference (Vysc−Vxg) is applied across the row electrode Xi and the row electrode Yi. This potential difference (Vysc−Vxg), not starting discharge itself, can immediately cause (transfer) “writing sustain discharge” between the row electrodes Xi and Yi with a trigger of the preceding writing discharge. Due to such address discharge, positive or negative wall charges are stored on the surface of the dielectric layer 106A (see FIG. 10) located on the discharge cell(s) in a quantity capable of causing sustain discharge only with later application of a sustain pulse Vs.
Thus, the “address discharge” is formed by (i) “writing discharge” selectively generated between the row electrode Xi and the column electrode Wj and (ii) “writing sustain discharge” triggered by the “writing discharge” and caused between the row electrode Xi and the row electrode Yi.
On the other hand, the discharge cells turned out in image display (i.e., in the sustain discharge period) are not made to cause address discharge and hence no discharge is caused between the row electrodes Xi and Yi of the discharge cells and no wall charges are stored as a matter of course.
The sustain discharge period follows the address period. In the sustain discharge period, the sustain pulse Vs is applied across the row electrodes Xi and Yi, thereby maintaining sustain discharge during this period in the discharge cell(s) subjected to the aforementioned writing. During the sustain discharge period, a voltage Vs2 set to substantially half the voltage value Vs of the sustain pulse Vs is applied to the column electrode Wj, so that sustain discharge can be stably started upon transition from the address period to the sustain period.
In the conventional AC-PDP and the driving method therefor, however, a column of discharge cells arranged along the vertical direction of the screen correspond to a single column electrode (data line). When the number of the column electrodes is increased following improvement in precision of the PDP or the like, therefore, the number of driving circuits (generally integrated) for supplying prescribed voltages to the column electrodes is also increased and hence the cost for the plasma display device is disadvantageously increased.